November 2, 2009 - Self-reported smoking during pregnancy underestimates the true number of pregnant smokers in Scotland by 17%, and results in a failure to detect 2400 pregnant smokers each year.

It is well known that self reported smoking during pregnancy is an inaccurate way to identify smokers. Yet it is still used widely by antenatal clinics to determine the smoking status of pregnant women and to refer them to smoking cessation services. The Scottish Government also relies on self-reported smoking figures to set targets and measure the success of smoking cessation services.

To address this issue, a team of researchers from Scotland assessed whether self-reported smoking during pregnancy is an accurate way of setting targets and identifying pregnant smokers in order to offer them smoking cessation services.The study involved a random sample (3475) of pregnant women from the West of Scotland and compared their self-reported smoking status at maternity booking with results of blood cotinine testing (to detect recent nicotine exposure) to estimate the number of undetected smokers. In total, 24.1% (839) of pregnant women reported being smokers compared to the cotinine-validated estimate of 30.1% (1046).

Therefore, approximately a fifth (207/1046) of cotinine-validated smokers were not detected by self-report and were not offered smoking cessation services, which translates to 2400 pregnant women a year.

Importantly, the use of self-reporting in Scotland results in twice as many pregnant smokers from more deprived areas going undetected each year compared with pregnant smokers from more affluent areas. The authors estimate that the true smoking prevalence for pregnant women in Scotland, after adjusting for area deprivation, maternal age and self-reported smoking is 28%, higher than the 23% based on self report data.

The researchers call for more accurate methods of identifying pregnant smokers, so that accurate data is used to inform policy and provide appropriate patient care.

Reliance on self reporting to identify pregnant smokers significantly underestimates the number of pregnant smokers in Scotland and results in a failure to detect over 2400 smokers each year who are therefore not offered smoking cessation services.